Prevails . The 'it' is entirely impersonal and general, and does not refer to any definite object. The use is frequent in Shakespeare, e.g.
'To revel it with him and his new bride,' Henry VI, Act iii. sc. 3,
and
'Lord Angelo dukes it well.' Measure for Measure , Act iii. sc. 2.
It is found also in Pope's
'Whether the charmer sinner it or saint it.' Volume 1